The present invention generally relates to processing received communication signals and particularly relates to interference cancellation during detection of a received signal's modulation type.
In response to an ever-increasing demand for wireless services, wireless providers continue exploring new ways to increase the capacity of current wireless networks. One way to increase network capacity, commonly referred to as frequency reuse, involves reusing the same frequencies across the wireless network. When a wireless network employs frequency reuse, multiple cells within the wireless network reuse predefined radio frequencies to transmit/receive wireless signals within the boundaries of each cell. Ideally, every cell in the wireless network reuses the same frequencies to maximize network capacity. However, this 1/1 frequency reuse plan results in significantly increased interference effects, particularly co-channel and adjacent channel interference effects. These effects cause poor speech quality, lower data throughput, call dropout, etc. As a result, current wireless networks may instead use a ¼ frequency reuse plan to reduce the interference while still obtaining some network capacity improvement.
Interference arising from frequency reuse becomes particularly problematic in communication networks where different communication signal formats are used for different kinds of services, or to achieve different data rates, etc. For example, GSM/EDGE (Global System for Mobile communications/Enhanced Data rates for Global Evolution) networks use both Gaussian Minimum Shift Keying (GMSK) modulation and 8-ary Phase Shift Keying (8PSK) modulation. A given receiver in such networks may be expected to detect the modulation type of an incoming received signal such that it properly adjusts its received signal processing.
Such detection is referred to as “blind” detection because the receiver is expected to determine the received signal's modulation type without being provided any explicit indication. A wrong guess on the receiver's part is costly in that nonsensical results flow from processing the received signal using the wrong modulation type assumption. Significantly, received signal interference, including co-channel and adjacent channel interference arising from aggressive frequency reuse, can seriously impair conventional blind detection processing. Such impairment can be particularly problematic in single-antenna receivers.